1. Field of the Invention
The present invention relates to a ferrule for optical connector which is one of components of an optical connector and which positions and secures an end face of an optical fiber, and making method thereof.
2. Related Background Art
One of methods of connecting ends of optical fibers to each other is a method of providing a connector structure at the ends of optical fibers. For constructing the connector structure at the ends of optical fibers, components called ferrules are used as members for positioning and securing the ends of optical fibers, facilitating the positioning of the ends to each other, and maintaining the fibers in a connected state. For example, MT connectors and MPO connectors are commonly known as connector standards using the ferrules. An example of such known connectors is one described in the Publication of U.S. Pat. No. 6,146,024.
Upon connection of optical fibers their cores in the central portions thereof need to be positioned with accuracy, and in these MT connectors and MPO connectors guide holes and guide pins are used for positioning the cores to each other. A pair of guide holes are bored in a connecting end face of each connector and guide pins are inserted into these guide holes to position a pair of optical connectors. There were, however, cases wherein upon coupling/uncoupling of the connectors the guide pins damaged the periphery of the opening portions of the guide holes to degrade the connection state, thereby increasing transmission loss. The ferrule for optical connector described in the Publication of aforementioned U.S. Pat. No. 6,146,024 is constructed in order to solve this problem so that a taper portion is provided around the opening portion of each guide hole.
The ferrule for optical connector provided with such taper portions can suppress the increase of transmission loss described above. The inventors invented a ferrule for optical connector that can realize far superior performance. An object of the present invention is to provide a ferrule for optical connector that is configured to effect the positioning with guide pins and guide holes and that can further reduce the connection loss upon connection of connectors and making method thereof.
A ferrule for optical connector according to the present invention is a ferrule comprising a fiber positioning hole, a pair of guide holes into which guide pins are inserted, and a connecting end face in which ends of the fiber positioning hole and the guide holes open, wherein a chamfer portion equivalent to a part of a surface of a body of revolution is formed at each guide hole on the connecting end face side, and wherein the connecting end face is formed so as to have an angle relative to a plane normal to center axes of the pair of guide holes.
In this structure, the provision of the chamfer portions can facilitate the insertion of the guide pins, prevent the damage of the connecting end face caused by the guide pins, and suppress the increase of connection loss due to the damage. The provision of the chamfer portions can suppress deformation of the rear ends of guides due to the guide pins and, in turn, degradation of the connection state between connecting end faces and thus can also restrain the increase of connection loss in this respect. In the present invention, further, the connecting end face is formed so as to have the angle relative to the plane normal to the center axes of the pair of guide holes, which can decrease degradation of characteristics due to reflection at the end face of optical fiber.
The making method of this ferrule for optical connector is making a chamfer portion equivalent to a part of a surface of a body of revolution by drilling or grinding process after making ferrule body having fiber positioning holes and guide holes by plastic molding. Such making method allows making a chamfer portion having a desired shape accurately. For example, this drilling or grinding process is performed with drill whose tip is made of hard metal or diamond or rotating grindstone.
Drilling or grinding process with drill or grindstone can ease to change the shape of the chamfer portion by changing the shape of drill tip or grindstone, general versatility of processing is increased and it can increased the manufacturing accuracy of chamfer portion. Further, if the connecting end face is angled and it is necessary for making the chamfer portion corresponding to the angle of the connecting end face, the chamfer portion may be made at preferred position according to the present invention. So the freedom of making the chamfer portion is highly increased.
It is preferable here that a center axis of each chamfer portion be parallel to the center axis of each corresponding guide hole, and positioned in an area extending from the plane passing through both center axes of the pair of guide holes toward the side where the base end side of the connecting end face exists. The expression xe2x80x9cthe area extending from the plane passing through both center axes of the pair of guide holes toward the side where the base end side of the connecting end face existsxe2x80x9d as used herein shall mean the overall area including the area occupied by such plane itself and the area extending away from such plane toward the side where the base end side of the connecting end face exists. Further, since the connecting end face formed to make an angle with the center axis of the guide hole have a tip end side and a base end side, the expression xe2x80x9cthe side where the base end side of the connecting end face existsxe2x80x9d indicates the side on which this base end side exists.
By adopting such structure, the chamfer portions are formed at preferred positions in the inclined connecting end face, whereby the areas around the chamfer portions can be prevented from chipping and whereby the distal ends of the guide pins can be guided into the guide holes with accuracy. As a consequence, the effects of the provision of the chamfer portions can be achieved with more certainty than in the case of the chamfer portions being simply formed, and the connection loss can be reduced more.
Further, it is preferable here that when the connecting end face is formed so as to have an angle of 8xc2x0 relative to the plane normal to the center axes of the two guide holes, the chamfer portions be formed so that an aperture size of each chamfer portion on the connecting end face is within a range of 1.05 to 2.0 times an inside diameter of the guide holes. When the aperture size of each chamfer portion is set within the range of 1.05 to 2.0 times the inside diameter of the guide holes, the effects of the provision of the chamfer portions can be achieved best. The setting in this range can accurately absorb fluctuations of the guide pins upon connection of connectors due to the tolerance of the ferrule itself and/or the tolerance of a housing if the ferrule is housed in the housing.
In another configuration, it is preferable that when the connecting end face is formed so as to have an angle of 8xc2x0 relative to the plane normal to the center axes of the two guide holes, a deviation amount between the center axis of each chamfer portion and the center axis of each guide hole be 50-300 xcexcm. When the deviation amount between the center axis of each chamfer portion and the center axis of each guide hole is set in the range of 50 to 300 xcexcm, the chamfer portions on the connecting end face can be set at preferable positions, which can maximize the effects of the provision of the chamfer portions.
It is also preferable that each chamfer portion be formed so that the center axis of each chamfer portion has an angle relative to the center axis of each corresponding guide hole. It is more preferable that his relative angle is set to be not more than the angle of the connecting end face relative to the plane normal to the center axes of the guide holes. Off course, these angles may set to be equal.
By adopting such structures, the guide pins can be smoothly guided into the guide holes by the chamfer portions and the chamfer portions can be made readily. In case of equalizing these angles, it becomes feasible to enhance the positional accuracy of the chamfer portions and the like and facilitate the formation of the chamfer portions.
Preferably, the ferrule may include the filler whose average particle size is not more than 20 xcexcm. More preferably, maximum particle size of the filler is not more than 20 xcexcm. Such filler may be silica. Including such filler can realize the smooth surface of the chamfer portion, so when the guide pin contacts the chamfer portion, the deformation of guide pin or chamfer potion can be restrained and excessive abrasion of drilling or grinding tools can be restrained. More preferably, the surface roughness of this chamfer portion is within the range between 0.01 to 2.0 xcexcm.